Immunocytochemical distribution of extracellular matrix receptors in human osteoclasts: A β3 integrin is colocalized with vinculin and talin in the podosomes of osteoclastoma giant cells

Human osteoclasts (OCLs) obtained from cell suspensions of surgically excised giant cell bone tumors (osteoclastomas) were attached to glass coverslips and analyzed by immunofluorescence with antibodies to integrins and cytoskeletal proteins. It was found that in OCLs (i) podosomes, identified by their F-actin core and by interference reflection microscopy, were predominantly found in a peripheral belt as described in avian OCLs; (ii) each F-actin core was surrounded by a ring of vinculin and talin; (iii) β₁ integrin was diffuse in the ventral membrane; (iv) β₃ integrin was distributed in intensely fluorescent rings surrounding F-actin cores; (v) β₂ integrin was absent; (vi) β₄ integrin was absent. The macrophages detected in the same coverslips displayed podosomes containing β₂ but not β₃, fibroblasts showed adhesion plaques positive for β₁ and β₃ but not for β₂, and platelets were intensely positive for β₃. These results indicate that OCLs produce an integrin complex that is absent in the monocyte-macrophage lineage.